VietNamNet Bridge – While hydroelectricity is considered as a “green” energy source, such projects along the Mekong River have been placing adverse impacts on fishery resources as well as people residing by this water body, experts argued.

The Mekong River stretches more than 4,800km through six countries: China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. It has the second biggest fish output in the world, after the Amazon River, said Nguyen Huu Thien, the former head of Vietnam’s National Advisory Group on assessing strategic environmental impacts of hydropower plants on the Mekong River’s mainstream.

About 20 percent of the global freshwater fish output, or 2.1 million tonnes, hail from the Lower Mekong Basin (LMB), according to a 2010 report on the Mekong River Commission Strategic Environmental Assessment of Hydropower on the Mekong Mainstream.

Other estimates said the river is home to 1,200 fish species. Notably, Vietnam’s Mekong Delta, where the river flows into the sea, harbours a particular diversity of species, 486, with various sizes from several metres to a few centimetres long.

Fishery resources play a crucial role in ensuring food security in the LMB, including Cambodia, Thailand, Laos, and Vietnam, which have the highest level of per capita freshwater fish consumption.

Around 2 million tonnes of fish and 0.5 million tonnes of other aquatic species are caught in the LMB every year in addition to 2 million tonnes of farmed products. Therefore, fisheries are pivotal to diversifying people’s sources of living, especially of lower income groups who have to rely on the river and its resources to earn their daily bread.

World researches indicate that hydropower dams affect ecological and hydrographical systems in rivers since they act as barriers to the movement of fish.

A study on the Amazon River showed that the presence of dams in this river’s basin hampered some catfish species from moving over long distances, resulting in a 70 percent decline in the haul in the lower section.

Meanwhile, most of the species that people catch in the Mekong River are migrants, thus the influence of hydropower dams on fish’s migration is undeniable. Besides, these facilities also interrupt the natural flood cycle familiar to aquatic species for thousands of years and make the river bed uninhabitable due to the loss of habitat and food sources.

Nguyen Huu Thien explained that the LMB and the Mekong Delta in particular has a flood and a dry season along with two alternated transitional periods. These periods are important to the entire eco-system as they act as a signal informing aquatic species that it is time to migrate, breed, or do other activities in their life cycle.

Hydropower dams’ storage and release of water will shorten or make transitional periods to disappear or turn the dry season into the flood one and vice versa. As a result, aquatic species will become confused about seasons and unable to follow their normal activities, he added.

The 2010 report also said hydropower dams will block the flow of alluvium, thus reducing the source of food for fish in coastal waters.

It is estimated that about 100 million tonnes of alluvium carrying along 16,000 tonnes of nutrition substances are left in coastal waters of this delta every year, helping the Mekong Delta has an annual marine product output of between 500,000-726,000 tonnes.

Hydroelectricity has long been considered as a “green” energy source since they do not emit greenhouse gases during operation, theoretically help control water currents, and prevent floods and droughts in downstream areas.

However, the development of these facilities along major river systems like the Mekong River needs to be thoroughly contemplated by all countries that it traverses.

Nguyen Nhan Quang, an expert on river basin management, said it is essential to clarify possible impacts of dams on migrant species, water currents, and the alluvium flow in order to avoid consequences of future hydropower projects and help countries in the LMB realise the Agreement on the cooperation for the sustainable development of the Mekong River Basin.

The Mekong River Commission reported that by 2013, there were at least 77 hydropower projects planned on Mekong River's tributaries and 11 mainstream hydropower projects/dams planned in the LMB, which is home to more than 60 million people.